1. Field of the Invention
The present invention relates to a lighting control system using a microcontroller, and to a lighting control method thereof, in particular, to the lighting control system and method for transmitting various electric powers to a lighting load by the microcontroller.
2. Description of Related Art
Refer to FIG. 1, which shows a schematic diagram of a conventional lighting control system. This kind of lighting control system has a light-dimming circuit 2, which is used to control an AC power to deliver a specific value of electric power to a lighting load 1. The light-dimming circuit 2 further includes a semi-conductor switching device 20 and a phase triggering circuit 22. This switching device 20 may be a well-known bi-directional control switch. The phase triggering circuit 22 usually comprises a variable resistor and a capacitor to generate trigger signals with variant time differences. The trigger signals are used to control the turn-on period of the semi-conductor switching device 20 during positive and negative half-cycle of the AC power. Therefore, variant electric powers are transmitted to the lighting load 1.
However, since the conventional system of this art is limited by its fundamental design, the turn-on period of the bi-directional control switch (such as TRIAC) may not be substantially adjusted for transmitting a full power or a predetermined minimal power to the lighting load. Moreover, the structure using a variable resistor to control light intensity may not be easily coupled with other electronic circuits to implement more desirable functions.
For preventing the above-mentioned drawback due to passive electric components, the light-dimming circuit 2 shown in FIG. 1 adopts circuits composed of semi-conductor electronic devices, for example, in U.S. Pat. No. 5,442,177. Thus the bi-directional control switch may be fully turned off or turned on within each AC half-cycle. In one further conventional art, for example, in U.S. Pat. No. 5,598,066, the light-dimming circuit 2 comprises an AC zero-crossing-point detection circuit to generate trigger signals and bring the bi-directional control switch into conduction with at least two different turn-on periods. So that, an incandescent lamp or a halogens lamp connected to this bi-directional control switch may display 30% or 100% of full light intensity within an AC-cycle. Furthermore, the circuits used in the bi-directional control switch may be incorporated with the circuits of daylight detection and motion detection. The lighting load of the above design may thus automatically deliver 30% or 100% of full light intensity in accordance with environmental conditions for the purpose of saving electric power.
However, the above-mentioned two arts have complicated circuit assembly. These arts of lighting control are implemented by analog-digital hybrid circuits that adopt lots of discrete analog and digital integrated circuits. Therefore, they cause high manufacturing cost and even result in high electric power consumption. For example, the power consumption in a light dimming system according to U.S. Pat. No. 5,598,066 is measured around 30 W at standby state. This quantity of electric power loss is even larger than the electric power dissipated at a low brightness state of the lighting load. Therefore, this conventional art of light control system with analog-digital hybrid circuits is not in compliance with the purpose of electric power saving.